package main

import (
	"fmt"
	"log"
	"sync"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
)

// grain-pool.go
//
// Migration Note:
//   This file has been migrated to use uint64 cart keys internally (derived
//   from the new CartID base62 representation). For backward compatibility,
//   a deprecated legacy map keyed by CartId is maintained so existing code
//   that directly indexes pool.grains with a CartId continues to compile
//   until the full refactor across SyncedPool / remoteIndex is completed.
//
//   Authoritative storage: grains (map[uint64]*CartGrain)
//   Legacy compatibility:  grainsLegacy (map[CartId]*CartGrain) - kept in sync.
//
//   Once all external usages are updated to rely on helper accessors,
//   grainsLegacy can be removed.
//
// ---------------------------------------------------------------------------

var (
	poolGrains = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_grains_in_pool",
		Help: "The total number of grains in the pool",
	})
	poolSize = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_pool_size",
		Help: "The total number of mutations",
	})
	poolUsage = promauto.NewGauge(prometheus.GaugeOpts{
		Name: "cart_grain_pool_usage",
		Help: "The current usage of the grain pool",
	})
)

// GrainPool interface remains legacy-compatible.
type GrainPool interface {
	Apply(id CartId, mutation interface{}) (*CartGrain, error)
	Get(id CartId) (*CartGrain, error)
}

// Ttl keeps expiry info
type Ttl struct {
	Expires time.Time
	Grain   *CartGrain
}

// GrainLocalPool now stores grains keyed by uint64 (CartKey).
type GrainLocalPool struct {
	mu       sync.RWMutex
	grains   map[uint64]*CartGrain // authoritative only
	expiry   []Ttl
	spawn    func(id CartId) (*CartGrain, error)
	Ttl      time.Duration
	PoolSize int
}

// NewGrainLocalPool constructs a new pool.
func NewGrainLocalPool(size int, ttl time.Duration, spawn func(id CartId) (*CartGrain, error)) *GrainLocalPool {
	ret := &GrainLocalPool{
		spawn:    spawn,
		grains:   make(map[uint64]*CartGrain),
		expiry:   make([]Ttl, 0),
		Ttl:      ttl,
		PoolSize: size,
	}
	cartPurge := time.NewTicker(time.Minute)
	go func() {
		for range cartPurge.C {
			ret.Purge()
		}
	}()
	return ret
}

// keyFromCartId derives the uint64 key from a legacy CartId deterministically.
func keyFromCartId(id CartId) uint64 {
	return LegacyToCartKey(id)
}

// storeGrain indexes a grain in both maps.
func (p *GrainLocalPool) storeGrain(id CartId, g *CartGrain) {
	k := keyFromCartId(id)
	p.grains[k] = g
}

// deleteGrain removes a grain from both maps.
func (p *GrainLocalPool) deleteGrain(id CartId) {
	k := keyFromCartId(id)
	delete(p.grains, k)
}

// SetAvailable pre-populates placeholder entries (legacy signature).
func (p *GrainLocalPool) SetAvailable(availableWithLastChangeUnix map[CartId]int64) {
	p.mu.Lock()
	defer p.mu.Unlock()
	for id := range availableWithLastChangeUnix {
		k := keyFromCartId(id)
		if _, ok := p.grains[k]; !ok {
			p.grains[k] = nil
			p.expiry = append(p.expiry, Ttl{
				Expires: time.Now().Add(p.Ttl),
				Grain:   nil,
			})
		}
	}
}

// Purge removes expired grains.
func (p *GrainLocalPool) Purge() {
	lastChangeTime := time.Now().Add(-p.Ttl)
	keepChanged := lastChangeTime.Unix()

	p.mu.Lock()
	defer p.mu.Unlock()

	for i := 0; i < len(p.expiry); i++ {
		item := p.expiry[i]
		if item.Grain == nil {
			continue
		}
		if item.Expires.Before(time.Now()) {
			if item.Grain.GetLastChange() > keepChanged {
				log.Printf("Expired item %s changed, keeping", item.Grain.GetId())
				if i < len(p.expiry)-1 {
					p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
					p.expiry = append(p.expiry, item)
				} else {
					// move last to end (noop)
					p.expiry = append(p.expiry[:i], item)
				}
			} else {
				log.Printf("Item %s expired", item.Grain.GetId())
				p.deleteGrain(item.Grain.GetId())
				if i < len(p.expiry)-1 {
					p.expiry = append(p.expiry[:i], p.expiry[i+1:]...)
				} else {
					p.expiry = p.expiry[:i]
				}
			}
		} else {
			break
		}
	}
}

// GetGrains returns a legacy view of grains (copy) for compatibility.
func (p *GrainLocalPool) GetGrains() map[CartId]*CartGrain {
	p.mu.RLock()
	defer p.mu.RUnlock()
	out := make(map[CartId]*CartGrain, len(p.grains))
	for _, g := range p.grains {
		if g != nil {
			out[g.GetId()] = g
		}
	}
	return out
}

// statsUpdate updates Prometheus gauges asynchronously.
func (p *GrainLocalPool) statsUpdate() {
	go func(size int) {
		l := float64(size)
		ps := float64(p.PoolSize)
		poolUsage.Set(l / ps)
		poolGrains.Set(l)
		poolSize.Set(ps)
	}(len(p.grains))
}

// GetGrain retrieves or spawns a grain (legacy id signature).
func (p *GrainLocalPool) GetGrain(id CartId) (*CartGrain, error) {
	grainLookups.Inc()
	k := keyFromCartId(id)

	p.mu.RLock()
	grain, ok := p.grains[k]
	p.mu.RUnlock()

	var err error
	if grain == nil || !ok {
		p.mu.Lock()
		// Re-check under write lock
		grain, ok = p.grains[k]
		if grain == nil || !ok {
			// Capacity check
			if len(p.grains) >= p.PoolSize && len(p.expiry) > 0 {
				if p.expiry[0].Expires.Before(time.Now()) && p.expiry[0].Grain != nil {
					oldId := p.expiry[0].Grain.GetId()
					p.deleteGrain(oldId)
					p.expiry = p.expiry[1:]
				} else {
					p.mu.Unlock()
					return nil, fmt.Errorf("pool is full")
				}
			}
			grain, err = p.spawn(id)
			if err == nil {
				p.storeGrain(id, grain)
			}
		}
		p.mu.Unlock()
		p.statsUpdate()
	}

	return grain, err
}

// Apply applies a mutation (legacy compatibility).
func (p *GrainLocalPool) Apply(id CartId, mutation interface{}) (*CartGrain, error) {
	grain, err := p.GetGrain(id)
	if err != nil || grain == nil {
		return nil, err
	}
	return grain.Apply(mutation, false)
}

// Get returns current state (legacy wrapper).
func (p *GrainLocalPool) Get(id CartId) (*CartGrain, error) {
	return p.GetGrain(id)
}

// DebugGrainCount returns counts for debugging.
func (p *GrainLocalPool) DebugGrainCount() (authoritative int) {
	p.mu.RLock()
	defer p.mu.RUnlock()
	return len(p.grains)
}

// UnsafePointerToLegacyMap exposes the legacy map pointer (for transitional
// tests that still poke the field directly). DO NOT rely on this long-term.
func (p *GrainLocalPool) UnsafePointerToLegacyMap() uintptr {
	// Legacy map removed; retained only to satisfy any transitional callers.
	return 0
}